Multilayer sheet articles comprise individual substrates bonded together with adhesives. Typically, cellulosic sheet, e.g., paperboard, cardboard, paper, coated paper, films, are bonded together with waterborne adhesives to form containers for consumer products such as cups, food containers, cases, cartons, bags, boxes, envelopes, wraps, clamshells, and the like.
Heavier basis weight substrates provide better strength and thermal insulation to the article than lower basis weight substrates. However, there is an effort to decrease the basis weight of the substrates to become more environmentally and economically sound.
Reducing the basis weight negatively impacts thermal insulation and strength of the article. While microspheres are known to improve thermal insulation properties, the substrate thickness is the primary source for the thermal insulation of the article.
Microspheres have been also added to paper pulp for making reduced-weight paper and thin cardboards, as described in WO 2008/084372. However, the resultant papers are prone to out-of plane buckling when subjected to vertical stresses.
In order to improve the strength of low basis weight substrates, Adhesive Level Effect on Corrugated Board Strength-Experiment and FE Modeling teaches to increase the amount of adhesives interposed between the substrates. However, increasing the amount of the adhesive in the article lengthens the drying time and thereby decreases manufacturing speed. Long drying time or heaters must be used to drive the water out of the substrates, which increases energy consumption.
The present invention improves the shortcomings of packages with reduced basis weight, through the use of a waterborne adhesive composition with expanded microspheres. The present invention provides an environmentally sound package that provides sufficient strength and thermal insulation to the reduced basis-weight substrates upon which it is being applied.